The present invention is directed to methods and devices for operating a printing unit. At least one counter-pressure cylinder and one transfer cylinder constitute a printing position. The cylinders are driven at controlled speeds.
In the course of driving cylinders or groups of cylinders by the use of separate drive mechanisms, for example in satellite printing units, process-related unwinding differences between the pairs of cylinders can occur. These unwinding differences are dependent on the cylinder contact pressure, on the number of active printing positions, on the thickness of the dressings carried by the cylinders, on the type of cylinders, or even on the producer, or source of the dressing itself, whether the friction gear is embodied without or with bearer rings, on the radii of the bearer rings, or on the radius ratios of the friction gear as a whole.
This unwinding difference can result, in part, in considerable and, with changing conditions, in considerably varying output effects between the cylinders, or groups of cylinders. This is undesirable, since it results in asymmetries in the output layout, in different outputs, depending on the conditions and modes of operation, or even in overloads of the motors and regulators.
Cylinders of a rotary printing press with bearing rings are known from DE 195 01 243 A1. The bearing rings of the satellite cylinder are rotatably seated for the purpose of reducing the output transfer.
In WO 00/41887 A1, a compensating friction gear, in the form of bearing rings of reversed radius ratios, is superimposed on a friction gear with cylinders which are in process-related frictional contact. The normal force between the cylinders placed against each other is set in such a way that a value of a difference between the power consumption of the motors driving the cylinders is minimal.
DE 195 27 199 A1 shows a drive mechanism for a printing unit. A forme cylinder can be driven at varying circumferential speeds as a function of a contact of the printing forme with a counter-pressure cylinder. A circumferential speed, which differs from that of the counter-pressure cylinder, occurs in a phase of the cylinder rotation in which there is no printing contact between the forme and the counter-pressure cylinder.
The object of the present invention is directed to providing methods and devices for operating a printing unit.
In accordance with the invention, these objects are attained by driving a printing unit, which includes at least one counter-pressure cylinder and one cooperating transfer cylinder, in a manner such that the speeds of the two cylinders may be different. The counter-pressure cylinder is driven by a drive motor. The speed of the counter-pressure cylinder may be varied as a function of the absorbed output or of the electrical output of that drive motor. A deviation between the speeds of the two cylinders may be sensed [means of the characteristics of claim 1, 3, 5 or 12, and 13, 14 or 22].
The advantages which can be obtained by the invention consist, in particular, in that a sufficiently good unwinding of the printing cylinders takes place, which unwinding is, to a large extent, a function of the contact pressure and/or of the number of the active printing positions, or of the thickness of the dressing and/or the type or the manufacturer of the dressing. With changing configurations of the printing positions and/or the dressings, and in particular with changing configurations of the printing blankets on the transfer cylinders, the print quality is not, or is only slightly, reduced.
In principle, it is possible to determine a suitable defined difference in the cylinder circumferential speeds at different modes of operation and/or for various dressings, which defined differences can be stored in a memory, for example, and, depending on the mode of operation/or dressing, can be forced on and maintained during production.
A minimization of the fluctuation range of the motive or of the generative output of the drive motor takes place in an advantageous manner by the regulation, in accordance with the present invention, of the leading or of the trailing of the rpm, or of the circumferential speed, of at least one of the cylinders with respect to at least one oppositely located cooperating second cylinder as a function of the output of the drive motor, either produced or received, via the friction gear.
The above mentioned regulation can be employed, in particular, in connection with printing units in which several transfer cylinders form printing positions with so-called satellite cylinders. For example, this regulation can be used in 5-cylinder printing units, in 9-cylinder satellite printing units, or in 10-cylinder satellite printing units.
The employment of the regulation is particularly advantageous for printing units with cylinders which roll off one another without the use of bearing rings. The satellite cylinder is operated in a leading or trailing manner, which manner of operation is a function of the power consumption, or of the output, of the drive motor assigned to it, with respect to the transfer cylinder cooperating with it. In the case of cylinders without bearing rings, the output is transferred exclusively by the cylinders themselves rolling off on each other. In case of a change of the configuration of a cylinder, in particular when changing the dressings on the transfer cylinders, for example dressings in the form of printing blankets with different conveying properties, which are so-called negatively, neutrally or positively conveying printing blanket, the required generative or motive output at the satellite cylinder is maintained within narrow limits by use of the regulation. In this way, an excess size of regulation and/or the danger of overloading regulating device and drive motors is reduced.
However, the regulation is also suitable for printing units with bearing rings which roll off on each other. In this case, a slippage between the bearing rings within defined limits, as discussed subsequently, is permitted.
In order to maintain a desired print quality, selectable lower or upper limits of the deviation of the number of revolutions, or of the circumferential speed of the satellite cylinder, from the circumferential speed of the cooperating transfer cylinders, are not downwardly or upwardly exceeded. This occurs simultaneously with the reduction of the generative or motive output at the satellite cylinder. The satellite cylinder is driven within these limits at its minimum absolute output, either generative or motive. These deviation limits can each be variously selected in connection with various materials to be imprinted, with various printing methods and with various demands made on quality. They range, for example for newspaper printing, at a deviation of xc2x10.01% to xc2x10.05% from the production, or circumferential speed of the cooperating cylinders.
This speed regulation is advantageous for printing units whose cylinders are driven in groups or which are driven individually by several mechanically unconnected drive motors. Such regulation is advantageous, for example, for 9-or 10-cylinder satellite printing units with one drive motor each per cylinder, for 9-or 10-cylinder satellite printing units with one drive motor for each forme cylinder-transfer cylinder pair and the satellite cylinder(s), and also for 9-or 10-cylinder satellite printing units with one drive motor each for each group of forme cylinder-transfer cylinder pairs.